Age-related macular degeneration (AMD) is a leading cause of irreversible blindness among elderly Americans, with devastating consequences for patients and healthcare costs. Reliable therapies are lacking for the estimated 85% of AMD patients that have non-exudative (dry) AMD (dAMD). This application interrogates a novel therapeutic strategy for these vulnerable patients based on the phytochemical sulforaphane. This compound is derived from cruciferous vegetables and has been extensively studied for its anti-cancer, anti- microbial, and anti-oxidant properties. There are ~ 30 clinical trials underway testing SFN for diseases ranging from prostate cancer to autism. Overwhelmingly, the pharmacological efficacy of SFN has been attributed to its capacity to restore redox homeostasis by activating Nrf2, a master anti-stress transcription factor. But, mounting evidence shows that Nrf2 expression and signaling are compromised with aging. In fact, post- mortem AMD eyes have reduced expression of Nrf2 in dysmorphic, macular retinal pigment epithelial (RPE) cells, and the RPE cells in aged mice have impaired Nrf2 signaling. We have recently discovered an unrecognized activity of SFN that is independent of Nrf2 and have exciting preliminary data demonstrating that SFN preserves vision in Nrf2 knockout mice challenged with an oxidative stress targeting the RPE. These data and our strong investigative team are uniquely positioned to determine the molecular and cellular mechanisms as well as the in vivo efficacy of this novel activity of SFN. The proposed studies will therefore focus on the Nrf2-independent activity of SFN. Mechanistically, we have shown that SFN protects RPE cells (+/- Nrf2) from stress by modulating mitochondrial fusion and fission dynamics. This novel activity has significant clinical implications as deficits in mitochondrial dynamics and metabolic capacity have been observed in primary RPE cells from AMD donor eyes. The specific aims of this application will test the following hypotheses: (1) SFN-mediated mitochondrial hyperfusion results from inhibiting the activity of the Drp1 GTPase that mediates mitochondrial fission; (2) SFN-mediated hyperfusion preserves mitochondrial function; and (3) SFN preserves vision and RPE integrity in subacute and chronic models of RPE mitochondrial oxidative stress (+/- Nrf2). The proposed experiments utilize a complementary set of innovative reagents and approaches including photoactivation localization microscopy (PALM) to track single molecule movements in polarized RPE cultures, super resolution structured illumination microscopy to analyze fusion/fission dynamics and mitophagy, acute and chronic mouse models of RPE mitochondrial stress in young and aged mice and psychophysical structure-function tests on live animals and post-mortem, histopathological analyses to measure RPE/retinal survival and pathology. Collectively, the proposed work engenders an unexplored therapeutic opportunity for SFN, with the promise to expand the clinical utility of this agent to AMD and other age-related diseases with impaired Nrf2 signaling.